prometheus-node-exporter: add procd status exporter

[vooon]

📦 Package Details

Maintainer: @dhewg

Description:

• Add procd service status metrics.
• PID metric may be used to determine if the process was restarted
• Exit code - to ignore some services stopped (e.g. when rc=0)

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🧪 Run Testing Details

• OpenWrt Version: SNAPSHOT
• OpenWrt Target/Subtarget: x86/64
• OpenWrt Device: KVM

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✅ Formalities

• I have reviewed the CONTRIBUTING.md file for detailed contributing guidelines.

If your PR contains a patch:

• It can be applied using git am
• It has been refreshed to avoid offsets, fuzzes, etc., using
• It is structured in a way that it is potentially upstreamable
  _{(e.g., subject line, commit description, etc.)
  We must try to upstream patches to reduce maintenance burden.}